Remove the tyre and inner tube.
Check for rough edges around the valve hole of the rim and smooth with emery paper.
Check that your rim tape is in place. If not, replace wit Velox brand.
Check that the spoke heads to not poke into the inner tube.
Fit a new tube with a metal valve.
When you put the inner tube back in, ensure that it points naturally to the hub, not at an angle. Threaded metal valves have a nut to secure the valve in position.
This is a fairly easy one to do yourself and good practice for puncture repairs.